The present invention generally relates to gas turbine engines, and more particularly, to the maintenance of compressor liner segment spacing.
A typical aircraft gas turbine engine includes a compressor for pressurizing air which subsequently is mixed with fuel and ignited in the combustor section with the resulting combustion gases powering the turbine. The compressor and turbine are surrounded by casings or liners through which air is either extracted or distributed.
In a typical compressor, an inner liner is concentric with a outer casing and mounts stator or variable vanes. The inner liner also surrounds the rotor blades of the compressor. The air generated by the compressor is at an extremely high temperature, therefore compressor liners are used to form an aerodynamic flowpath and to protect the casing structure from the flowpath environment.
The inner compressor liner is formed in segments around the circumference of the compressor. The liners are formed in two or more sections to eliminate large thermal stresses due to temperature differences between the casing and the liners. Because the liner is segmented, it allows recirculation leakage in between the segments which in turn reduces compressor performance. In order to reduce this leakage, spline seals are added between the liner segments.
Gap dimensions between the liner segments where the spline seals are located are determined by the thermal expansion of the liner segments. Because the gaps between the liner segments are required to be large to compensate for thermal close-down of the liner segments, keeping the spline seals engaged between the liner segments and functioning properly has become problematic.
In order to keep the liner segments in proper alignment, therefore maintaining the spline seals in between the liner segments, radial bolts have been previously used to fasten the liner segments to the outer casing. By fastening the liner segments to the outer casings, uniform spacing between the liners can be maintained. However, radial bolts require reinforcement on the outer casing and also on the liners to maintain structural integrity of the compressor. This additional reinforcement adds weight and complexity to the design, as well as making such liners more difficult to assemble and disassemble from the engine.
An alternate method of positioning liner segments is by forming a stop at the axial flange of each casing half in a circumferential groove in the casing which holds the liner segments. This method has also proven unsatisfactory in that forming a stop in the casing groove has required expensive machining operations, and also has proven to be inefficient.
Therefore, a need exists for an improved mechanism for maintaining uniform spacing between compressor liner segments that eliminates the aforementioned problems associated with radial bolts and casing stops. Further, there is a need for a segment liner spacing system in which the segments are relatively inexpensive to manufacture and easy to install.